The ? Block is one of the many blocks found in the Mario universe.
? Blocks are commonly seen floating in midair, often containing Gold Coins, Super Mushrooms or Fire Flowers.
In the Paper Mario Series, Red ? Blocks contain badges and yellow ones contain coins or items.
? blocks are sometimes invisible at first. They are turned visible by jumping into them (or using Watt in Paper Mario). Once they're visible, they can be used as stepping stones.
In Super Mario 64 DS, red ? blocks replace the red, blue, and green ! Blocks. They contain either Power Flowers or Bob-ombs, depending on character and hat status.
In the Mario Kart series, similar item blocks, called "Item Boxes" are found on every track, each containing an item to be used to assist you in the race. These blocks would appear again in Mario Tennis and Mario Power Tennis. Mario Kart: Double Dash introduced Double Item Boxes. There are also some Item Boxes knwon as Fake Item Boxes.
In New Super Mario Bros., red flying ? Blocks fly around the world map, moving to different levels every time Mario or Luigi die or complete a level. Five items can be inside: a Fire Flower, 1-Up Mushroom, Mini Mushroom, Mega Mushroom, or a Blue Koopa Shell.
They reappeared in Mario Hoops 3-on-3, where they took the form of ? Panels that appeared in various places around each court. Dribbling the ball over one of these panels results in acquiring a Coin, a Red Coin, or a Mushroom or Poison Mushroom.
They are not to be confused with ! Blocks, which are similiarly floating blocks.